The present invention relates to sensor systems in general, and more particularly, to piezoelectric and piezoeresistive sensor cables for anomaly and/or deformation detection and localization.
Sensor detection systems currently enjoy a variety of applications. For example in the automotive industry, sensor devices that trigger safety functions such as airbags need to be particularly reliable and fail-safe. In U.S. Pat. No. 5,404,128 a presence-detecting sensor positioned in a seat of a vehicle to detect the presence of a human being is disclosed. The sensor is interconnected to control means that control functioning of the vehicle. The sensor is a piezoelectric element for detecting vibrations and is provided with a self-diagnostic function. One of these self-diagnosis means is to position a termination resistance between electrodes, and pass an electric current through the sensor. If the sensor is severed, this can be detected as the circuit is open so that no current flows. If a short circuit occurs along the sensor, this is also detected by the zero voltage drop thereacross.
Still further, published GB patent application GB 2317707 entitled xe2x80x9cCABLE TESTING ARRANGEMENTxe2x80x9d describes a cable fault detection system comprising an oscillator connected to an electrode of a cable such that the cable forms an impedance (inductance or capacitance) element of an oscillating circuit. The fault detection system operates within a bandwidth outside that of the sensor operation. By filtering signals the sensor and fault detection activities may operate simultaneously without interfering with one another.
These systems, however, are limited to anomaly detection. Thus, a need exists for an anomaly detection and location sensor system.
A sensor cable having a first end and a second end includes an outer shield, a piezoresistive portion positioned within the outer shield, a controlled resistive portion positioned within the piezoresistive portion, a dielectric portion positioned within the controlled resistive portion, and a conductive core positioned within the dielectric portion. More particularly, the sensor cables includes a conductive core positioned within the cable, a dielectric layer concentrically positioned radially outward and adjacent the conductive core, a controlled resistive layer concentrically positioned radially outward and adjacent the dielectric layer, a piezoresistive layer concentrically positioned radially outward and adjacent the resistive layer, and an outer shield concentrically positioned radially outward and adjacent the piezoresistive layer.
Deformation of the cable creates a change in resistance between the shield and the controlled resistive layer. Electrical parameters between the controlled resistive layer and the shield are detectable at each end of the cable. The location of the deformation is deducible by comparing detected electrical parameters indicative of the change in resistance at each corresponding end of the cable.